Massive multiple input multiple output (MIMO) is a wireless transmission technology using multiple antennas at a base station or a relay, in which interference between user equipment (UE) signals is spatially controlled through the same beamforming, so that a large number of UE devices are simultaneously serviced by using the same amount of wireless resources, and also the power consumption per UE device is reduced by a reciprocal of the number of antennas.
However, in the case of the massive MIMO, when beamforming is applied to each UE device in a wide service area such as the conventional three sectors, in order to implement the massive MIMO technology by the frequency division duplexing (FDD), the UE device needs to estimate massive MIMO channel state information (CSI) and feed back the estimated Massive MIMO CSI to a base station such that the base station uses the CSI in determining weights. Therefore, such a great amount of CSI feedback makes it difficult to implement the massive MIMO technology.
In order to solve this problem, a method in which a sector of the conventional three-sector system is divided into a plurality of beam sectors and beam division multiple access (BDMA), as a technology for the conventional multiuser (MU)-MIMO, is provided in the beam sector has been proposed. The BDMA technology not only effectively divides frequency/time resources but also spatial resources in a mobile communication system, and allocates orthogonal beams to UE devices, allowing for multiple access. That is, the BDMA technology allows terminals located in similar positions to communicate by sharing a single beam.